Internal temperature of a physical object can be determined from the object's external surface temperature as measured using conduction-based devices or radiation-based devices. The object being measured is assumed to have an interior with an internal temperature in a substantially steady state and an external surface. There are many examples where it is desirable to know the internal temperature of such an object Examples: monitoring the safety level inside a tank holding hazardous chemicals, determining whether livestock are ready for insemination, or checking the temperature of a patient in a hospital.
This background section of this invention specification reviews temperature measurement solutions for the body of a human being as that is a common application of temperature measurement of an object and illustrates the prior art technology.
For conduction-based measurement, the thermometer probe must be in contact with the body the entire time during the measurement. The temperature measurement is aimed at measuring the temperature of internal body tissues, which is very close to the core body temperature. The measuring device is brought into contact with external tissues, such as the skin or more preferably, somewhat thermally insulated external tissues, such as the throat. It can take about 10 minutes for convection from the external tissue to bring the measuring device to equilibrium temperature at which the internal tissue temperature can be measured. Such a long measurement time is inconvenient for the patient.
In order to shorten measurement time, a predictive algorithm can be used. However, often this incurs a tradeoff of less accuracy for shortened measurement time.
On the other hand, infra-red (IR) radiation is a very fast method of temperature measurement. Again, the most accurate measurement is made from protected external tissues, therefore IR thermometers typically measure tympanic (eardrum) temperature.
However, such a measurement is considered invasive, which may disturb the patient. Also, there is a limitation due to the fact that ear canal is not always straight so there is no direct line of sight to the eardrum. Furthermore, when using radiation for direct skin temperature measurement, the measurement is affected by environment temperature.
A variation on conduction-measurement is a thermometer that in permanent contact with the patient's skin. This solution can result in high accuracy due to the fact that the permanently-attached thermometer has had the time to reach thermal equilibrium by the time the temperature measurement is made.
However, having the thermometer attached to the body is problematic. It is inconvenient for the patient to “carry” such a device for a long time, especially for babies.
The present invention also makes use of the principle of prolonged contact for highly-accurate conduction. However only a passive component is in contact with (worn by) the patient. The actual measurement is done either by an IR measurement device that reads the temperature from the passive conductive contact device or by suitable electronic device in the case the passive component includes heat transducers.
It has been established by an earlier invention by the present inventors, U.S. Pat. No. 6,280,397, entitled “HIGH SPEED ACCURATE TEMPERATURE MEASURING DEVICE” (2001) that heat flux emitted from a human body, i.e., from blood vessels to the skin, together with the temperature measured on the skin may be used to accurately derive the body's inner temperature. The current invention also relates to using heat-flux in temperature measurement, however the analysis is done in steady state rather than in transient state. In steady state, the heat flux is constant and all the time derivatives of the temperatures are zero. Thus, a simplified model can be used to derive the internal temperature. The current invention further differs from the earlier patent in that it reads temperatures relating to a surface in persistent contact with the surface of the measured object, thereby enabling accurate calculation of the inner body temperature.
In summary, it is a main object of the present invention to provide a means for convenient, fast, accurate internal temperature measurement.
Other objects and advantages of the present invention will become apparent after reading the present specification and reviewing the accompanying drawings.